Various key retaining devices are known in the art for transmitting torque between a cylindrical shaft and an encircling member journalled thereon. Such coupling devices not only prevent relative rotation between the members, but also serve to maintain their relative axial positions. Most often these key retaining devices are disposed at one end of the shaft in order to permit easier removal and serviceability of the encircling member. However, design problems become apparent with many of these devices when the ends of the shaft are relatively inaccessible. For example, it is often not practical or even possible to machine elongated key slots in either the shaft or the surrounding member to be coupled to it. These elongated slots would not only be expensive to produce, but would appreciably reduce the structural integrity of the members. In addition, these elongated slots are totally unacceptable in those instances where the shaft is rotatably supported on bearings at its opposite extremities.
The use of tapered pins, set screws, and Woodruff keys represent other solutions for coupling a tubular member to a shaft. However, these solutions suffer the frequent disadvantage that the key members could vibrate out with use unless a key retaining system is incorporated therewith.
Further, these key members normally require an opening in the tubular member which serves as a stress riser therein so that the tubular member must be increased in thickness at increased expense in order to resist the forces tending to spread the opening apart.